This retrospective-prospective study will identify mother-offspring pairs where prenatal estrogen exposure occurred and will determine the cancer incidence among these mothers and offspring. Two control groups of mother-offspring pairs will be identified and the cancer incidence among these women and their offspring will be compared to that in the at-risk group. One group will be based on physician-matched controls, the second control group will be selected using Connecticut birth registration data. Cancer experience will be determined through linking the names of members of the cohorts to patients reported to the Connecticut Tumor Registry. All cancer sites will be considered with particular attention on reproductive system cancers. To date, more than 900 exposed mother-offspring pairs and 700 physician-matched control pairs have been identified and detailed information has been abstracted from their prenatal records and related birth certificates. These activities have been accomplished for an additional 100 unmatched physician controls. A second control group of 1150 mother-offspring pairs had been selected. All study mothers have been followed through the use of City Directories to determine person-years-at-risk.